• PDF / 596,211 Bytes
• 11 Pages / 439.37 x 666.142 pts Page_size
• 103 Downloads / 246 Views

DOWNLOAD

REPORT

---

Selective Oxidation of Chromium by O2 Impurities in CO2 During Initial Stages of Oxidation Soraya Bouhieda • Fabien Rouillard Vincent Barnier • Krzysztof Wolski

•

Received: 25 May 2012  Springer Science+Business Media New York 2013

Abstract This study shows that the corrosion behaviour of 12 wt% Cr steel in CO2 at 550 C is determined in the first stage of oxidation by reaction with O2 impurities. Depending on the amount of theses impurities and the thermal ramp rate, selective oxidation of chromium could lead to the formation of a protective chromium-rich oxide. An oxidation model describing qualitatively the nature of the oxide layer formed in the initial period of oxidation is presented. From these observations, surface engineering processes for protecting 9–12 wt% chromium steels from fast corrosion rate have emerged. Keywords Ferritic–martensitic steels
Carbon dioxide
Selective oxidation
Impurity
Oxygen

Introduction In the framework of the development of sodium fast reactors in France, carbon dioxide integrated in the Brayton cycle is proposed as new cycle energy conversion S. Bouhieda
F. Rouillard (&) Laboratoire d’Etude de la Corrosion Non Aqueuse, CEA, DEN, DPC, SCCME, 91191 Gif-sur-Yvette, France e-mail: [email protected] S. Bouhieda e-mail: [email protected] V. Barnier
K. Wolski Laboratoire Claude Goux, UMR CNRS 5146, Centre SMS, Ecole des Mines de Saint-Etienne, 158 cours Fauriel, 42023 Saint-Etienne, France e-mail: [email protected] K. Wolski e-mail: [email protected]

123

Oxid Met

system to replace current steam generators. The main advantages of this cycle are the improvement of the reactor safety by suppressing the risk of the exothermic watersodium reaction, the improvement of the cycle compactness and the increase of the cycle efficiency. Ferritic–martensitic (F/M) steels with 9–12 wt% Cr are good candidates for heat exchanger application for many reasons: they have good mechanical properties up to 650 C, high thermal conductivity, low expansion coefficient and usually a lower cost as compared to austenitic steels. However, many studies have shown that their corrosion behaviour in CO2 at 550 C can dramatically affect their performance due to fast corrosion kinetics and strong carburization [1–9]. Few studies on the effect of the impurities present in CO2 on the corrosion behaviour were presented in the literature and it can be pointed out that only the effect of a high amount of oxygen (1–3 %) in CO2 was presented [10]. This study is interested in the effect of the impurities present in small amount (ppm) in CO2 gas on the corrosion behaviour. Indeed, it was shown in a previous article that impurities present in carbon dioxide strongly impact on the corrosion behaviour from the initial stages of oxidation [11] and that depending on the CO2 purity slow growing oxide scale could be formed on these F/M steels. In this study the impurity responsible for the corrosion behaviour of a 12 wt% Cr ferritic–martensitic steel (VM12) has been identified and discussion about phenomeno